Dawn–dusk asymmetry of dayside magnetic pileup and horizontal ion transport at Venus under different interplanetary magnetic field orientations

The interaction between the solar wind and the atmosphere of Venus leads to the formation of an induced magnetosphere, within which pronounced dawn–dusk asymmetries are observed in magnetic field pileup and ion transport. These asymmetries are known to depend on the orientation of the interplanetary magnetic field (IMF), but the underlying physical mechanisms governing this dependence remain incompletely understood. The aim of this study was to investigate how different IMF orientations influence magnetic field pileup, mathrm O ^+ ion distribution, and horizontal plasma transport in the induced magnetosphere of Venus, and to identify the dominant electromagnetic forces responsible for the resulting dawn–dusk asymmetries. We employed a multi-fluid magnetohydrodynamic (MHD) model to simulate the solar wind–Venus interaction under different IMF orientations. The model was used to analyze the spatial distribution of magnetic field strength, mathrm O ^+ ion number density, horizontal velocity, and ion flux. In addition, individual electromagnetic force components, including the motional electric field, the ambipolar electric field force, and the boldsymbol J B force, were quantitatively examined. The simulations show that when the IMF is not perpendicular to the solar wind flow, the dawnside, corresponding to the hemisphere toward which the IMF points in the simulation setup, exhibits stronger magnetic field pileup and enhanced horizontal plasma transport than the duskside. This dawn–dusk asymmetry weakens when the IMF orientation approaches perpendicularity to the solar wind. Force analysis reveals that the boldsymbol J B force is the primary driver of the asymmetric plasma transport. The magnetic field component normal to the planetary surface displays opposite signs on the dawn and dusksides, generating horizontal magnetic gradients and oppositely directed current density systems, which in turn produce asymmetric boldsymbol J B forces. These results demonstrate that the radial magnetic field structure and the resulting boldsymbol J B force play a critical role in controlling dawn–dusk asymmetries in plasma transport within Venus’ induced magnetosphere. The findings highlight the importance of electromagnetic forces, particularly the boldsymbol J B force, in shaping the structure and dynamics of the solar wind–Venus interaction under varying IMF orientations.